arch: relaunch setup after 2nd stage bootstrap, to recreate needed groups.
Fix bug when -b is specified and groups need to be created/modified.

Steps to reproduce:
```
$ sudo enter-chroot -n precise -u 0 groupdel hwaudio
Entering /usr/local/chroots/precise...
Unmounting /usr/local/chroots/precise...
$ sudo enter-chroot -n precise -b sleep 1
Entering /usr/local/chroots/precise...
Creating hwaudio group with GID 18...
wait: 476: Illegal number:
Unmounting /usr/local/chroots/precise...
```

 - env is only redefined after groups ID are checked
 - We do not want to silently ignore errors, so moving env redefinition earlier is not a good option
 - We fix the problem by checking if $pid is non-empty (should be safe in all cases)
tests/14-background: remove rc.local instead of making a backup copy of it.
arch: 30-audio test.
arch/aur: Install ca-certificates
audio: Put 32/64 compatibility definitions in separate header file; Fix for >=stabilize-5062.
Fix locking of bootstrap/snapshot tarballs.
edit-chroot: Fix spinner to check for command's exit status.
unmount: Remove ' (deleted)' from /proc/mount entries.

Try removing it, or not, in case somebody wants a mount point ending in ' (deleted)'.
Do not run upgrade test if some of the releases are not being tested.